1. Field of the Invention
The present invention relates to a projection lens and a projection apparatus, and more particularly to a projection lens suitable for magnifying and projecting an original image formed, for example, by a light valve and a projection apparatus using the same.
2. Description of the Related Art
Heretofore, projection display devices (projectors) that magnify and project images displayed on image display surfaces of light valves, such as liquid crystal display devices, DMDs (Digital Micro-mirror Device: registered trade mark), and the like, have been used when conducting presentations or the like. As for the lenses used in the projection display devices, wide angle lenses are in high demand because large screen sizes with short projection distances are often required. Further, there is a tendency that zoom lenses are preferred as the screen size needs to be adjustable with a high degree of freedom under limited installation conditions. As a wide angle projection zoom lens, for example, the lens described in Japanese Unexamined Patent Publication No. 2009-251316 may be cited.
Further, in the projection display devices, it is required that the quality of the projected image does not change largely when the projection distance is changed. Japanese Unexamined Patent Publication No. 2008-257005 describes a projection zoom lens whose object is to correct variation in the field curvature when the projection distance is changed. Japanese Unexamined Patent Publication No. 2011-145580 described a projection display apparatus whose object is to obtain an image which is in focus in a wide range through the projection onto a spherical or curved projection surface and the degree of curvature of the image surface due to field curvature is performed adjustable by changing the distance between two lens groups.